This invention relates to a photographic film spool and particularly to a photographic film spool comprising a pass-through type slit provided at about the center of a spool core so that a tongue-shaped end of a film may be inserted through the slit and a means provided in the slit for catching the perforations on the tongue-shaped end of the film.
As shown in FIG. 11, photographic film spools of conventional type are generally composed of catch claws 53 which are arranged on one inner wall surface 52a of the slit 52 provided at about the center of spool core 51 and is capable of catching perforations on the tongue-shaped end of a film and composed of film pressure rib 54 provided on the other inner wall surface 52b. Edges of both catch claws 53 and pressure rib 54 are slanted linearly toward the rear of the slit. When the tongue-shaped end of a film is inserted into the slit 52 from the film inlet 55, the perforations on the tongue-shaped end of a film are engaged with catch claws 53 and after their engagement, the perforations are caught by the catch claws when the film is pulled out slightly in the opposite direction.
In spools of this type, a film caught by catch claws 53 is regularly wound up around film contact surface 55a adjoining smoothly the inner wall surface 52a of a slit provided with catch claws 53, as shown by a solid line with an arrow mark `a`. Therefore, film contact surface 55a is shaped in a circular arc form so as not to bend any film to an acute angle. In contrast to the above, when the film is wound up in a regular manner, the film touches, after being wound around spool core 51 once, another film contact surface 55b adjoining the inner wall surface 52b of the slit provided with pressure rib 54. Therefore, as shown in the drawing, there may be no problem even if film contact surface 55b is so shaped stepwise as to form a sharp edge. However, when a film is erroneously wound up in the direction opposite to the regular winding direction as shown by a two-dot chain line with arrow mark `b`, the film is bent sharply at the intersecting point 56 of the slantingly-shaped film contact surface 55b and inner wall surface 52b of the slit. For example, after a film cartridge containing a film regularly wound up around a spool core is practically loaded into a camera and pictures are taken, there may be some occasions where the film rewinding handle of a camera is erroneously turned in the direction opposite to the regular winding direction when rewinding the film around the spool core. In addition to the above, if such a film rewinding is made at a low temperature such as in winter time, there is a risk that a breakage takes place on the portion of a film which contacts directly to aforesaid intersecting point 56.
This invention is to solve the above-mentioned problems.
It is, therefore, an object of the invention to provide a photographic film spool so devised as not to cause any risk of damaging films even in case that a film is reversely wound up around a spool core at a substantially low temperature.
In the conventional spool, as shown in FIG. 13, the radius of the spool core portion A forming slit 62 is smaller than that of circumferential portion B inside of flanges 66 and 66, which has caused a big step S formed on a boundary zone between both portions mentioned above. Therefore, when the film 63 is wound around spool core 61 after the tongue-shaped end 63b of the film 63 is caught in slit 62, the tongue-shaped end 63b is wound around the portion A where the slit is formed, while, the main portion of the film 63 following the tongue-shaped end 63b is wound around the circumferential portion B whose radius is greater. Consequently, the film 63 is deformed as shown in the figure, being affected by aforesaid step S, and both corners 63c and 63c of the film end 63a are lifted, which has caused a risk that the emulsion side of the film wound around the spool once is scratched by aforesaid both corners 63c and 63c.
The present invention is for solving aforesaid problems and its object is to provide a photographic film spool whose spool core enables a film to be wound around the spool without being deformed.